The Adeptus Astartes (commonly known as Space Marines, and colloquially as Angels of Death) are one of the most elite and feared fighting forces in the Imperium of Man. The primary unit of organisation is the Chapter, a self-contained army fully equipped with its own transport, non-combatant support staff, etc. There are around a thousand Chapters, each comprising a thousand Space Marines. There are far too few Space Marines to form the Imperium's main military forces; instead they operate as highly mobile strike forces. They are entrusted with the most dangerous missions, such as lightning raids behind enemy lines, infiltration, and tunnel fighting[5]. Through selection, training, and conditioning, Marines are physically, mentally, and spiritually superior to any other Imperial soldier.[4]

The Legions took part in the Great Crusade, during which the lost Primarchs were rediscovered and given command of their respective Legion. The Crusade, lasting for two centuries, ended with the treachery of one of the Primarchs, Horus, who lead at least half of the Legions in a rebellion known as the Horus Heresy against the Emperor. In the final battle for control of the future of mankind, Horus was slain by the Emperor. With the rebellion defeated, those Legions which had sided with Horus were driven into the Eye of Terror.

The Legions which had remained loyal were eventually reorganised according to the dictates of the Codex Astartes, in the event known as the Second Founding. Each Legion was divided into several autonomous Chapters, which remain the primary unit of the Space Marines to the current day.

Successive foundings over the millennia have created new Chapters. There are now around a thousand Chapters in existence, each Chapter ultimately descending from one of the loyalist Legions.

To some extent, the Chapters maintain the traditions and character of the Legion they descend from. Chapters adhere to the Codex Astartes in differing degrees, some regarding any deviation from it as virtual heresy; others, notably the Black Templars, Blood Angels, Space Wolves, and Dark Angels, only following the Codex in the broadest matters.[1][3][5]

Organisation

The Adeptus Astartes is comprised of autonomous Chapters, each of which is a complete army in itself, possessing its own transport, Warp-capable spacecraft, non-combatant personnel, and fortress-monastery based on a planet or fleet. There are roughly a thousand Chapters, each led by a Space Marine with the rank of Chapter Master. A Chapter's fighting force numbers a nominal 1000 Marines, divided into ten companies, each of which is commanded by a Captain. Companies are further divided into squads of ten battle-brothers.[4]

The Chapter Masters owe their allegiance to the Emperor. Ultimately, the Chapter is subject to the orders of the highest-ranking among the Adeptus Terra, although only in a general sense.[6]

Chapters are monastic communities in nature; for most of the Marines, the Chapter is their world, and the only contact they have with outsiders is in battle.

Tactical Organisation

The traditional Codex Chapter is tactically organised into a number of different types of squad: Tactical, Assault, and Devastator. The squad types are equipped and trained to fulfil a specific battlefield role, each of the three types designed to complement each other on the battlefield to make a far more effective whole. In addition to these three squad types, veterans can be formed into Veteran or Terminator Squads, while the initiate Marines are formed into Scout squads.

Terminator squads are drawn from the best and most experienced warriors of the entire Chapter. The veterans wear the uniquely powerful Terminator Armour. These squads are formed when circumstances necessitate the concentration of the Chapter's most capable warriors and potent equipment into one or more heavily-armed and powerful units.[7]

Chapter cult

A Chapter cult is an integral aspect of a Space Marine Chapter. Every Space Marine belongs to the Chapter's cult, and accordingly, every Marine of a Chapter is a spiritual brother as well as a brother-at-arms. These warrior cults emphasise honour, comradeship, and strength. Chapter cults, often thousands of years old, have each developed their own distinct traditions, and in many cases these cults pre-date the Imperial Cult, the official religion of the Imperium. Each Space Marine cult is unique and autonomous, ministered by an inner priesthood of warriors known as Chaplains. The practices of Space Marine cults, rumored to be barbaric and bloody, serve to make Space Marines all the more feared by the mass of humanity.

Specialist Space Marines

Equipment

The primary individual weapons of the Space Marines is the boltgun and its pistol variant, the bolt pistol.

The distinctive Power Armour is worn by all Marines in battle. Some members of the Chapter's first company may instead be armoured in the heavier Terminator Armour. Carapace armour is worn by Scouts instead of power armour. There is also a fourth type of armour called Artificer armour, worn by most Marines who have served three centuries for the Emperor or performed a notably brave action in battle.

Recruitment and Training

Recruits are chosen from the best warriors among humanity. Naturally, this makes Feral Worlds prized recruitment grounds, as such harsh and primal conditions produce the best warriors. However, Hive Worlds are considered the ideal source of potential recruits, the populace of the lower levels composed of some of the most murderous scum in the human Imperium. Whole gangs of hive scum are sometimes hunted down and captured for recruitment. Among the most valued traits in a recruit are aggression and psychotic-level killer instinct. Much more rarely, certain Civilised Worlds are also recruited from.[4][6]

The potential recruit is first subjected to testing, including tissue compatibility tests and psychological screening. Relatively few get past this initial selection process. Those that do pass are termed "neophytes", and the process continues with the surgery, indoctrination, conditioning, and training that will make them Marines.

The surgical process takes a great deal of time. The recruit receives implants, along with chemical- and hypnotherapy, and training necessary for allowing the functioning and development of the implanted organs. The implants transform their bodies and minds and give them inhuman abilities - making them capable of spitting acidic venom, absorbing the memories of the dead by eating their flesh, darkening their skin to protect it from radiation, and operating for long periods without sleep by switching off parts of their brains at a time. After this implantation process and the associated training, the recruit becomes an "initiate".

Intense indoctrination and conditioning strengthens the recruit's resolve and increases mental capabilities, honing them into dedicated and merciless warriors. After more general training, they join the Chapter as full "brothers".[2]

Daily Routine

Space Marines have very organised daily routines including combat training, prayer, and indoctrination sessions with very little free time. This lends itself well to the disciplined and monastic nature of the Space Marines.